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How do I test for radon?

By Radon411 Editorial TeamUpdated How we research

Short answer

Use a short-term test kit in the lowest lived-in level of your home, or hire a qualified tester: close windows and doors 12 hours before, set the device at least 20 inches off the floor away from drafts, leave it at least 48 hours, then mail it to the lab. A high result gets a follow-up test.

Next step: pick the right test for your home. Which test to use

The quickest way to test is with a , which stays in the home from two days to 90 days depending on the device; a of more than 90 days is more likely to show the year-round average. Every radon test should run for a minimum of 48 hours.

Keep during a short-term test: windows closed, doors closed except for normal entry and exit, and no fans that bring in outside air. Follow the kit's instructions, record the start and stop times, and send the device to the lab right away.

What to do next: get a kit or book a tester this week, and when the result comes back, read it against the testing steps below or with the interpreter.

How to test your home for radon, step by step

  1. Get a test

    Low-cost do-it-yourself kits come by mail and from hardware stores and other retailers, and some state radon programs and local health departments hand out free ones. Use a device from a qualified laboratory.

  2. Close the house

    For a test of 2 to 4 days, keep windows and outside doors closed for at least 12 hours before you start and for the whole test, apart from normal coming and going.

  3. Place the device

    Put it in the lowest lived-in level, in a room used regularly but not the kitchen or bathroom, at least 20 inches above the floor, away from drafts, high heat, high humidity and exterior walls.

  4. Start the test and note the time

    Follow the kit's instructions and write down the start date and time.

  5. Leave it alone

    Leave the kit in place for as long as the package says, and never less than 48 hours; some devices need longer.

  6. Stop, seal and mail

    Write down the stop date and time, reseal the package and send it to the lab right away.

  7. Read the result

    Results come back within a few days or weeks. Use the decision steps below, or the radon level interpreter.

Short-term or long-term test?

Table comparing a short-term radon test, a long-term radon test and a continuous radon monitor: how long each runs and what each is for.
Read this figure as text
TestHow long it runsWhat it is for
Short-term testStays in the home from 2 to 90 days, depending on the device, and for a minimum of 48 hours.A faster screening result. Because radon levels vary from day to day and season to season, it is less likely than a long-term test to tell you the year-round average.
Long-term testStays in the home for more than 90 days.It is more likely than a short-term test to tell you the home's year-round average radon level.
Continuous monitorLogs readings for the whole test, run as a short-term or a long-term test under the same durations in EPA guidance.Logs a graph over time, so you can see trends and spot anomalies rather than a single number.
The two lengths of radon test, and continuous monitors.

A stays in the home for two days to 90 days, depending on the device; a stays more than 90 days. The trade is speed against accuracy. Radon levels vary from day to day and season to season, so a short-term test is less likely to capture the year-round average, and the longer the test, the better the result reflects your home and how you live in it. Most people start short. For the full timing, see how long a radon test takes.

Where to put a radon test

Placement do's and don'ts
DoDo not
Test the lowest lived-in level: the basement if it is used, otherwise the first floorTest in a kitchen, bathroom, laundry room or furnace room
Use a room people use regularly, such as a living room, den or bedroomTest in a closet, stairway, hallway or crawl space
Raise it at least 20 inches off the floor; about three feet up in the middle of the room also worksPlace it near drafts, high heat, high humidity or exterior walls
In a multi-unit building, test the lowest level within your unitLeave it anywhere it could be moved or disturbed

For a home sale, the test goes in the lowest level that could be used regularly, finished or not, because a buyer may live lower in the house than the seller does. More on placement is in where should a radon test be placed.

Keeping the test valid

A radon test measures the house as it normally sits closed up. mean all windows closed, doors closed except for normal entry and exit, and no fans or machines bringing in air from outside. Heating and cooling run as usual.

During a short-term test
AllowedAvoid
Normal coming and going through outside doorsLeaving windows or doors open
Heating and air conditioning fans that recirculate airFans or other machines that bring in air from outside
Small exhaust fans for short periods, and a radon system's own fanTests of just 2 or 3 days during unusually severe storms or high winds
Living in the house as usualMoving or disturbing the device

Testing done wrong can give an inaccurate result and mean testing again, and interfering with the device or with closed-house conditions can invalidate the result and is illegal in some states. See can a radon test be manipulated.

What to do with the result

Flowchart of EPA's radon testing steps: take a short-term test; at or above 4 pCi/L follow up with a long-term or a second short-term test; then fix the home or consider fixing based on the result or the average of the two tests.
Read this figure as text

  1. 1Step 1: Take a short-term test.

    • Below 4 pCi/LEven if your test result is below 4 pCi/L, you may want to test again sometime in the future.
    • At or above 4 pCi/LIf your result is at or above 4 pCi/L, take a followup test to be sure.

  2. 2Step 2: Follow up with either a long-term test or a second short-term test.

    • Long-term testFor a better understanding of your year-round average radon level, take a long-term test.
    • Second short-term testIf you need results quickly, take a second short-term test. If your first short-term test result is more than twice EPA's 4 pCi/L action level, you should take a second short-term test immediately.

  3. 3Step 3: Decide whether to fix your home.

    • After a long-term testFix your home if your long-term test result is 4 pCi/L or more.
    • After a second short-term testConsider fixing your home if the average of your first and second test is at or above 4 pCi/L.
The testing steps after a first short-term test.

If the first result is high, the next step is a follow-up test: long-term for a better picture of the year-round average, or a second short-term test if you need an answer quickly. If the first result is more than twice the 4 , take the second short-term test immediately. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. If you later start using a lower floor, retest on that level.

Home sales use three short-term options instead, each with steps against interference: see the radon testing guide.

Questions about testing for radon

How do you test for radon in a basement?

If the basement is lived in or used regularly, that is where the test goes. Place the device in a room used regularly, at least 20 inches above the floor, away from the furnace room, laundry and exterior walls, with the house closed up.

How do radon tests work?

Passive devices, such as charcoal canisters and alpha-track detectors, sit in the air for a set time and then go to a laboratory. Active devices, continuous monitors, measure and record radon themselves, and many produce a report that shows unusual swings during the test.

Can I open windows during a radon test?

Not during a short-term test. Keep windows and outside doors closed as much as possible, and for a 2- to 4-day test close them at least 12 hours before the start as well.

How long does a radon test take?

At least 48 hours, and some devices need longer, such as a 7-day charcoal canister. Short-term tests stay 2 to 90 days and long-term tests more than 90 days. See how long a radon test takes.

Where can I get a radon test kit?

Hardware and home improvement stores, mail order, state radon programs, local or county health departments and some American Lung Association offices; your state may offer free or discounted kits. See free radon test kits.

How do you pass a radon test?

By lowering the radon, not the reading. A test that is interfered with can be thrown out. If the level is high, a mitigation system lowers it; see how to reduce radon.

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